Big difference. Little Bunny is a dwarf fountain grass (Pennisetum) , and will only get about 8-12" tall, not counting the flowers. It stays very compact, and is slow to leaf out in spring. Little Kitten is a Miscanthus variety and will eventually grow about 2-2 1/2' tall and wide, not counting flowers. It is not as compact as LB and has more of a weeping appearance. Also slow to leaf out, but not as slow as LB. LK is small for a Miscanthus, but much larger than LB.

If you are looking for small grasses, don't overlook Blue Fescue, Festuca glauca, one of the finest grasses available and very easy to find for cheap prices. Also easy to grow from seed. Plus it's evergreen.

I love my 'Little Bunny' because it was a gift from a special online friend but for overall garden worthiness the small Fescues can't be beat. I have 'Elijah Blue', 'Golden Toupee' and one that is much less blue than 'Elijah' that I don't know the name of. They are blooming now and are sooooooo cute and completely trouble free. They look great near the front door where the extended time of looking bad for the fountain grasses would be a distraction.

'Golden Toupee' is less vigorous and hasn't bloomed but is still very cute.